Contributions to Palaeontology. 



125 



In the same fragment of rock with the glabella, there 

 is a pygidium which I have presumed to belong to this 

 species. The axis is broad and prominent, marked by 

 about five rings besides the articulating one ; the lateral 

 lobes slope abruptly downwards, then curving they spread 

 in a broad flattened border (which is everywhere incom- 

 plete in the specimen); each side is marked by four ribs, 

 exclusive of the anterior one ; the two forward ribs are 

 divided through a part of their length, and the four 

 appear as gentle undulations in the border. 



This species possesses the essential characteristics of glabella 

 given by Dr. Owen for Dikelocephalus, except the slight conver- 

 gence of the sides ; and I have therefore referred it to that genus. 



The glabella, frontal limb and fixed cheeks resemble D . pepinensis ; 

 but the occipital ring in this one is more convex, and bears a spine ; 

 the occipital furrow is not so direct, while the posterior glabellar 

 furrows are more oblique : the second or median pair of furrows can 

 be traced across the glabella, while the anterior ones are slight 

 indentations in the margin, like the anterior and middle ones of D. 

 pepinensis. The dorsal furrow is more sharply impressed at the 

 sides ; turning rectangularly in front of the glabella, which is more 

 truncate, and separated by a narrower furrow from the more convex 

 frontal limb. 



These features are important distinctions, since in this one the 

 approach to the Genus Conocephalites, in the form of glabella 

 and glabellar furrows, is very perceptible. The pygidium has the 

 general expression of D. minnesoteiisis, being somewhat more convex, 

 but the minor characters are very different. 



This species occurs at Trempaleau in calcareo-magnesian sandstone, 

 near the middle of the formation. 



